Controle de Meloidogyne incognita em genótipos de tomateiro com extrato de semente de abacate

Abstract

The root-knot nematodes are pathogens of great economic importance for many craps, as tomato, for promoting a reduction in crop productivity. Thus, control methods are required and the use of plant extracts is gaining emphasis due their compounds with nematicide and resistance induction properties. The objective of this work was evaluate the control of Meloidogyne incognita in susceptible and resistant tomato plants treated with avocado seed extract (Persea americana Mill.) incorporated into the hydrogel. To obtain the extract, avocado seeds were cut and left in methanol for 24 h and passed through two vacuum filtering. The obtained solution was evaporated on a rotary evaporator and resuspended in distilled water containing Tween 80 (0.6%) to give concentrations of 100, 200, 400, 800 and 1.000 mg L-1 of red color (RE) and brown color (BE) extract. The control treatment was distilled water + Tween 80 (0.6%). Hatching of juvenile second stage (J2) and motility and mortality of J2 were evaluated. From the in vitro results, we selected the most efficient concentration in controlling nematode, incorporating the hydrogel and dried in an oven. Then, this material at different doses (0; 0.1; 0.25; 0.5; 0.75 and 1.0 g pit1) were added to the soil before the transplantation of the tomato. Three days after transplanting was made the inoculation with 2.067 eggs and J2 of M. incognita. Thirty days after inoculation were evaluated: relative chlorophyll content (SPAD index), total volume of root, number of galls and eggs mass, viability of the egg mass, number of eggs and J2 per root and 100 cm3 of soil. With the data obtained from this test in a greenhouse, a new experiment was carried out from the dose that provided the best control of the nematode. This was then added to extract pits containing different concentrations (0, 1.000, 2.000, 4.000, 6.000, and 8.000 mg L-1) in the hydrogel. After 30 days of inoculation with 2.184 eggs and J2 of M. incognita, there were the same described above ratings. For in vitro assays, the extracts promoted a reduction of J2 hatched, with the concentration of 1.000 mg L-1 of RE, the most effective in this reduction. The mobility and mortality of J2 were not affected by different concentrations of the extracts. In vivo, referring to the first assay, the dose of 1.0 g pit-1 controlled the nematode in susceptible plants, and therefore was chosen for use in the second assay. In this latter, the concentration of 8.000 mg L-1 was the most effective to control M. incognita.